Add device.getDirectory

[commandblockguy]

Adds a method to get the list of variables on a device.

This PR also adds support for receiving fragmented virtual packets and an expectAny method for receiving a virtual packet of unknown type.

It also makes several changes to parameter handling:

• Adds a public function for getting parameters from the device
• Allows non-numerical parameters to be constructed and destructed
• Fixes a bug in which an unrecognized parameter caused parsing to fail, as the code always expected a size to be provided, despite this not being the case when the device doesn't return a value for the parameter.
• Fixed a test case which relied on this bug
• Changed the return type of destructParameters to be an object rather than an array and to only include valid parameters
• Updated the test cases to use the new return format

I've only tested this on the CE, so it will probably need additional testing before being merged.